Compliant mooring technology to separate buoy motion from in-line current meter observations

To separate buoy motion effects from current meters and other sensors on the mooring line, compliant elastic elements have been used in the mooring directly under the buoy. This approach was used in the Massachusetts Bays Program to separate surface buoy motion from VACM current meters below. the elastic elements. Recently a mooring designed to measure waves with a surface following buoy was instrumented with an ADCP and water property sensors. Compliant elastic elements were used at the top of the mooring to allow the buoy to move freely with the waves without having to accelerate the mooring and deeper instrumentation. An ADCP was mounted near the bottom in an upward looking configuration. 0.5 kN of additional flotation (120 lbf) at the bottom of the elastic elements kept the lower part of the mooring taut to minimize motion. The elastic elements provided about 1.3 kN (300 lbf.) of mooring pretension, and, depending on the horizontal current and the wave activity, the tension at the buoy could rise to about 3.5 kN (800 lbf.). Computer modeling of the mooring showed no vertical and minimum horizontal motion in the lower part of the mooring and reasonable tensions that would allow the buoy to follow the waves. Data from the accelerometer in the buoy, the SeaCats in-line and ADCP near the bottom were of high quality. The mooring was recovered by releasing a float from mid-depth that brought a line to the surface from below the elastic elements to allow the mooring (with sensors) and anchor to be retrieved.